Subsurface safety valves are commonly installed as part of the production tubing within oil and gas wells to protect against unwanted communication of high pressure and high temperature formation fluids to the surface. These subsurface safety valves are designed to shut in fluid production from the formation in response to a variety of abnormal and potentially dangerous conditions.
As built into the production tubing, subsurface safety valves are typically referred to as tubing retrievable safety valves (“TRSV”) since they can be retrieved by retracting the production tubing back to surface. TRSVs are normally operated by hydraulic fluid pressure, which is typically controlled at the surface and transmitted to the TRSV via hydraulic control lines. Hydraulic fluid pressure must be applied to the TRSV to place the TRSV in the open position. When hydraulic fluid pressure is lost, the TRSV will transition to the closed position to prevent formation fluids from traveling uphole through the TRSV and reaching the surface. As such, TRSVs are commonly characterized as fail-safe valves, as their default position is closed.
However, as TRSVs are often subjected to years of service in severe operating conditions, failure of the TRSV is possible. For example, a TRSV in the closed position may eventually form leak paths. Alternatively, a TRSV in the closed position may not properly open when actuated. Because of the potential for operational problems in the absence of a properly functioning TRSV, it is vital that the malfunctioning TRSV be promptly replaced or repaired. Since they are incorporated into the production tubing, however, repairing or replacing a malfunctioning TRSV requires removal of the entire production tubing, which can be an expensive undertaking.
To avoid the costs and time of repairing or replacing a malfunctioning TRSV, a wireline retrievable safety valve (“WLRSV”) may instead be installed in the TRSV and operated to provide the same safety function as the a TRSV. WLRSVs are typically designed to be lowered into the wellbore from the surface via wireline and are then locked inside the original TRSV. This approach can be a much more efficient and cost-effective alternative to pulling the production tubing to replace or repair the malfunctioning TRSV. One common obstacle in using WLRSVs, however, is how to provide hydraulic pressure to the WLRSV for proper operation once installed.